Monitoring Activity	Monitoring Date
Air Quality	1-hr TSP at AMS5	3, 7, 13, 19, 25 and 31	3, 9, 14, 17, 23 and 28	2, 8, 14, 20, 26 and 30
1-hr TSP at AMS6	3, 7, 13, 19, 25 and 31	3, 9, 14, 17, 23 and 28	2, 8, 14, 20, 26 and 30
24-hr TSP at AMS5	6, 12, 18, 24 and 28	2, 8, 11, 16, 22 and 28	1, 7, 13, 19, 23 and 29
24-hr TSP at AMS6	6, 12, 18, 24 and 28	10, 11, 16, 22 and 28	1, 7, 13, 19, 23 and 29
Noise	3, 13, 19, 25 and 31	9, 14, 23 and 29	7, 14, 20 and 26
Water Quality	3, 5, 7, 10, 12, 14, 17, 19, 21, 24, 26, 28 and 31	2, 4, 7, 9, 11, 14, 16, 18, 21, 23, 25, 28 and 30	2, 5, 7, 9, 12, 14, 16, 19, 21, 23, 26, 28 and 30
Chinese White Dolphin	11, 12, 14, and 18	23, 24, 25 and 26 May	28, 29, 30 and 31
Mudflat Monitoring (Ecology)	3, 4	-	-
Mudflat Monitoring (Sedimentation rate)	28	-	-
Site Inspection	5, 12, 19 and 28	2, 9, 17, 25 and 30	7, 14, 21 and 30

Environmental Monitoring	Parameters	Limit Level (LL)
Air Quality	1-hr TSP	0
24-hr TSP	1
Noise	L_{eq (30 min)}	0
Water Quality	Suspended solids level (SS)	0
Turbidity level	0
Dissolved oxygen level (DO)	0
Dolphin Monitoring	Quarterly Analysis (March 2025 to May 2025)	1

Environmental Monitoring	Description	Monitoring Station	Frequencies	Remarks
Air Quality	1-hr TSP	AMS 5 & AMS 6	At least 3 times every 6 days	While the highest dust impact was expected.
24-hr TSP	At least once every 6 days	--
Noise	L_eq_(30mins)_, L₁₀_(30mins)and L₉₀_(30mins)	NMS 5	At least once per week	Daytime on normal weekdays (0700-1900 hrs).
Water Quality	�P Depth �P Temperature �P Salinity �P Dissolved Oxygen (DO) �P Suspended Solids (SS) �P DO Saturation �P Turbidity �P pH	�P Impact Stations: IS5, IS(Mf)6, IS7, IS8/IS8(N), IS(Mf)9 & IS10(N), �P Control/Far Field Stations: CS2(A) & CS(Mf)5, �P Sensitive Receiver Stations: SR3(N), SR4(N)/ SR4(N2), SR5(N), SR10A(N) & SR10B(N2)	Three times per week during mid-ebb and mid-flood tides (within �� 1.75 hour of the predicted time)	3 (1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth is less than 6 m, in which case the mid-depth station may be omitted. Should the water depth be less than 3 m, only the mid-depth station will be monitored).
Dolphin	Line-transect Methods	Northeast Lantau survey area and Northwest Lantau survey area	Twice per month	--
Mudflat	Horseshoe crabs, seagrass beds, intertidal soft shore communities, sedimentation rates and water quality	San Tau and Tung Chung Bay	Once every 3 months	--

Parameter (unit)	Water Depth	Action Level	Limit Level
Dissolved Oxygen (mg/L)	Surface and Middle	5.0	4.2 except 5 for Fish Culture Zone
Bottom	4.7	3.6
Turbidity (NTU)	Depth average	27.5 or 120% of upstream control station��s turbidity at the same tide of the same day; The action level has been amended to ��27.5 *and* 120% of upstream control station��s turbidity at the same tide of the same day�� since 25 March 2013.	47.0 or 130% of turbidity at the upstream control station at the same tide of same day; The limit level has been amended to ��47.0 *and* 130% of turbidity at the upstream control station at the same tide of same day�� since 25 March 2013.
Suspended Solid (SS) (mg/L)	Depth average	23.5 or 120% of upstream control station��s SS at the same tide of the same day; The action level has been amended to ��23.5 *and* 120% of upstream control station��s SS at the same tide of the same day�� since 25 March 2013.	34.4 or 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes; The limit level has been amended to ��34.4 *and* 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes�� since 25 March 2013

3 Environmental Monitoring and Audit

3.1 Implementation of Environmental Measures

3.1.1 Details of site audit findings and the corrective actions during the reporting period are presented in Appendix F.

3.1.2 A summary of the Implementation Schedule of Environmental Mitigation Measures (EMIS) is presented in Appendix E. Most of the necessary mitigation measures were implemented properly.

3.1.3 Regular marine travel route for marine vessels were implemented properly in accordance to the submitted plan and relevant records were kept properly.

3.1.4 Dolphin Watching Plan was implemented during the reporting period. No dolphins inside the silt curtain were observed. The relevant records were kept properly.

3.2 Air Quality Monitoring Results

3.2.1 The monitoring results for 1-hour TSP and 24-hour TSP are summarized in Tables 3.1 and 3.2 respectively. Detailed impact air quality monitoring results and relevant graphical plots are presented in Appendix G. The existing air quality monitoring location AMS6 �V Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021 and resumed on 7 August 2024. Average flow rate is used for calculation of 24-hr air quality results of AMS6 during August 2024 due to unstable electricity supply on site.

Table 3.1 Summary of 1-hour TSP Monitoring Results Obtained During the Reporting Period

Reporting Period	Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
Mar 2025	AMS5	100	67-122	352	500
Mar 2025	AMS6	79	49-110	360
Apr 2025	AMS5	100	61-130	352
Apr 2025	AMS6	100	73-122	360
May 2025	AMS5	109	85-125	352
May 2025	AMS6	91	74-105	360

Table 3.2 Summary of 24-hour TSP Monitoring Results Obtained During the Reporting Period

Reporting Period	Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
Mar 2025	AMS5	33	18-53	164	260
Mar 2025	AMS6	40	25-71	173
Apr 2025	AMS5	42	22-97	164
Apr 2025	AMS6	88	27-245	173
May 2025	AMS5	32	20-40	164
May 2025	AMS6	33	25-49	173

3.2.2 No Action and Limit Level exceedances of 1-hr TSP were recorded at AMS5 and AMS6. No Action and Limit Level exceedances of 24-hr TSP were recorded at AMS5. No Limit level exceedances of 24-hr TSP was recorded at AMS6 whereas One Action Level exceedance of 24-hr TSP was recorded at AMS6.

3.3 Noise Monitoring Results

3.3.1 The monitoring results for construction noise are summarized in Table 3.3 and the monitoring results and relevant graphical plots for this reporting period are provided in Appendix H.

Table 3.3 Summary of Construction Noise Monitoring Results Obtained During the Reporting Period

Reporting period	Monitoring Station	Average L_{eq (30 mins)}, dB(A)*	Range of L_{eq (30 mins)}, dB(A)*	Action Level	Limit Level L_{eq (30 mins)}, dB(A)
Mar 2025	NMS5	66	62-69	When one documented complaint is received	75
Apr 2025		61	57-67
May 2025		60	59-62

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.3.2 No Action/Limit Level exceedances for noise were recorded during daytime on normal weekdays of the reporting period.

3.3.3 Other noise sources during the noise monitoring included aircraft/helicopter noise, construction activities by other parties and human activities nearby.

3.4 Water Quality Monitoring Results

3.4.1 Impact water quality monitoring was conducted at all designated monitoring stations during the reporting period. Impact water quality monitoring results and relevant graphical plots are provided in Appendix O.

3.4.2 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

3.4.3 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

3.5 Dolphin Monitoring Results

Data Analysis

3.5.1 Distribution Analysis: line-transect survey sightings data were integrated with a Geographic Information System (GIS), QGIS (3.42.3), to visualise and interpret spatial and temporal distribution patterns within the two survey areas (NEL and NWL). As no dolphins were sighted, no distribution analysis was conducted.

3.5.2 Encounter rate analysis: monthly encounter rates of Chinese White dolphins, i.e., the number of sightings per 100 km of survey effort on the transect lines (STG) and the total number of dolphins sighted per 100 km of survey effort on the transect lines (ANI) were calculated for both NEL and NWL survey areas, to compare to baseline and other monitoring conducted for this project. Dolphin encounter rates were also calculated using total survey effort (on transect lines plus the effort transiting between lines) for comparison to the AFCD long-term marine mammal monitoring data.

3.5.3 To compare this quarterly period with the HZMB baseline monitoring period, encounter rates were calculated using effort conducted during Beaufort Sea State 3 or better. The average encounter rate of sightings (STG) and average encounter rate of dolphins (ANI) were calculated from all six line-transect surveys conducted in NEL and NWL areas and compared to the six surveys conducted in the same area for the baseline period.

3.5.4 To compare this quarterly period with AFCD long-term marine mammal monitoring data, encounter rates were calculated using effort conducted during Beaufort 3 or better. The average encounter rate of sightings (STG) and average encounter rate of dolphins (ANI) were calculated from all six line-transect surveys plus the transit length between lines, conducted in NEL and NWL areas.

3.5.5 Quantitative grid analysis of habitat use was conducted by plotting sightings of Chinese White dolphins recorded during this quarterly period onto 1km²grids superimposed across both NWL and NEL survey areas. Sighting densities (number of sightings per km²) and dolphin densities (total number of dolphins per km²) were then calculated for each 1 km by 1 km grid using an inbuilt function of the GIS software. As no dolphins were sighted, there were no data to plot.

3.5.6 Sighting density grids and dolphin density were assessed to account for the amount of survey effort conducted within each grid. The total amount of survey effort spent in each grid was calculated by examining how many times each grid was surveyed during the survey period, e.g., 50 passages across a specific grid resulted in 50 units of effort being assigned to that grid. Once effort was calculated for each grid, sighting and dolphin densities were calculated accordingly. As no dolphins were sighted, no density analysis was conducted.

3.5.7 Sighting density (SPSE) and dolphin density (DPSE) thus represent the number of sightings and dolphins, respectively, per 100 units of survey effort. If a 1km² grid also contained land, the percentage of the sea area was calculated using GIS tools, and SPSE and DPSE values adjusted accordingly. The following formulae were used to estimate SPSE and DPSE in each 1km²grid within the study area:

SPSE = ((S / E) x 100 / SA%

DPSE = ((D / E) x 100 / SA%

S = total number of on-effort sightings

D = total number of dolphins from on-effort sightings

E = total number of units of survey effort

SA% = percentage of sea area

As no dolphins were sighted, no density analysis was conducted.

3.5.8 Behavioural analysis: the behaviour of dolphins sighted during vessel surveys were assigned to a category, e.g., feeding, milling/resting, traveling, socialising, and recorded in the sighting database. These data were mapped in the GIS system to visualise which activities and behaviours occurred within the study area, so that important areas for different dolphin activities could be identified. As no sightings were recorded, no behavioural analysis was conducted for this quarter.

3.5.9 Ranging pattern analysis; the location of individually identified dolphins that were recorded during the 3-month baseline monitoring period were obtained from the dolphin sighting database. The home range for individual dolphins was calculated using a fixed kernel method, using the Animove plug-in in QGIS and the R statistical package. As no sightings were recorded, no home range analysis was conducted for this quarterly period.

Summary of Survey Effort and Dolphin Sightings

3.5.10 During the period of March to May 2025, six line-transect vessel surveys were conducted in NWL and NEL areas. All transect lines in each area were surveyed twice per month.

3.5.11 From these surveys, a total of 808.9 km of survey effort was collected, with 770.27 km (95.22%) of the total survey effort being conducted under favourable weather conditions (i.e., Beaufort Sea State 3 or better with visibility of more than 5km). Total survey effort conducted in NEL and NWL was 312.57 km and 496.33 km, respectively.

3.5.12 Of the 808.9km of total survey effort, 602.62 km was conducted on the transect line and 206.28 km of effort was conducted while transiting between transect lines. Observers continuously monitored the area in front of the survey vessel both while travelling the transect lines and when in transit between transects. A summary table of the survey effort is shown in Annex I of Appendix J.

3.5.13 No dolphins were recorded during the monitoring surveys conducted between March to May 2025. Since monitoring for this project began (2012), this is the second March-May quarterly period during which no sightings were recorded (the previous quarterly period that recorded no sightings was March-May 2022). Two other quarterly periods during this project's impact monitoring, also did not record any sightings (June-August 2021 and September-November 2022).

Encounter Rate

3.1.

3.2.

3.3.

3.4.

3.5.

3.6.

3.7.

3.8.

3.5.14 During this quarterly period, no dolphins were recorded while surveying the transect lines under favourable conditions (Beaufort 3 or better) (Table 3.4). The encounter rates averaged across all surveys were compared to the baseline monitoring period (September-November 2011) (Table 3.5).

Table 3.4 Dolphin Encounter Rates (Sightings Per 100 km of Survey Effort) During Reporting Period (March 2025 to May 2025)

SURVEY AREA	DOLPHIN MONITORING DATES	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
SURVEY AREA	DOLPHIN MONITORING DATES	Primary Lines Only	Primary Lines Only
Northeast Lantau	Set 1: March 11th / 12th	0.00	0.00
	Set 2: March 14th / 18th	0.00	0.00
	Set 3: April (23rd/24th May)	0.00	0.00
	Set 4: April (25th/26th May)	0.00	0.00
	Set 5: May 27th / 28th	0.00	0.00
	Set 6: May 29th / 30th	0.00	0.00
Northwest Lantau	Set 1: March 11th / 12th	0.00	0.00
	Set 2: March 14th / 18th	0.00	0.00
	Set 3: April (23rd/24th May)	0.00	0.00
	Set 4: April (25th/26th May)	0.00	0.00
	Set 5: May 27th / 28th	0.00	0.00
	Set 6: May 29th / 30th	0.00	0.00

Table 3.5 Comparison of average dolphin encounter rates from impact monitoring period (March 2025 to May 2025) and baseline monitoring period (September �V November 2011)

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)		Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
	March - May 2025	September - November 2011	March - May 2025	September - November 2011
Northeast Lantau	0.00	6.00 �� 5.05	0.00	22.19 �� 26.81
Northwest Lantau	0.00	9.85 �� 5.85	0.00	44.66 �� 29.85

Notes:
1) The encounter rates deduced from the baseline monitoring period have been recalculated based only on survey effort and on-effort sighting data made along the primary transect lines under favourable conditions.

2) �� denotes the standard deviation of the average encounter rates.

3.5.15 To facilitate comparison with the AFCD long-term monitoring results, encounter rates were also calculated for this quarterly period using both sightings recorded on the transect lines and while transiting between them. No sightings were recorded therefore, the sightings encounter rate (STG) and total number of dolphins encounter rate (ANI) in NWL and NEL were both 0.

3.5.16 In NEL, the dolphin encounter rates (both STG and ANI) in the present three-month impact monitoring period were both 0. Dolphin sightings within NEL have been rarely recorded during this quarterly period throughout this project's monitoring period; dolphin sightings have only been recorded in March-May 2013 and March-May 2024 (Table 3.6). Since this project's monitoring began, dolphins have been largely absent from the NEL area, which is consistent with AFCD long-term monitoring which records only two sightings in NEL since 2015 (all months of the year).

Table 3.6 Comparison of average dolphin encounter rates in the Northeast Lantau (NEL) survey area from all spring quarters (March-May) from the impact monitoring period and baseline monitoring period (September-November 2011).

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
September - November 2011 (Baseline)	6.00 �� 5.05	22.19 �� 26.81
March - May 2013 (HKLR03 Impact)	0.42 �� 1.03	0.42 �� 1.03
March - May 2014 (HKLR03 Impact)	0.00	0.00
March - May 2015 (HKLR03 Impact)	0.00	0.00
March - May 2016 (HKLR03 Impact)	0.00	0.00
March - May 2017 (HKLR03 Impact)	0.00	0.00
March - May 2018 (HKLR03 Impact)	0.00	0.00
March - May 2019 (HKLR03 Impact)	0.00	0.00
March - May 2020 (HKLR03 Impact)	0.00	0.00
March - May 2021 (TMCLKL Post-Construction)	0.00	0.00
March - May 2022 (TMCLKL Post-Construction)	0.00	0.00
March - May 2023 (HKLR03 Impact)	0.00	0.00
March - May 2024 (HKLR03 Impact)	0.48 �� 1.17	0.48 �� 1.17
March - May 2025 (HKLR03 Impact)	0.00	0.00

2) �� denotes the standard deviation of the average encounter rates.

3.5.17 In NWL, the dolphin encounter rates (both STG and ANI) in this quarterly period in 2025 were both 0. A complete absence of dolphins in the NWL area during this quarterly period is unusual. Since this project's monitoring began, only one other quarterly period did not record any dolphins; March-May 2022 (Table 3.7).

Table 3.7 Comparison of average dolphin encounter rates in the Northwest Lantau (NWL) survey area from all spring quarters (March-May) from the impact monitoring period and baseline monitoring period (September-November 2011).

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
September - November 2011 (Baseline)	9.85 �� 5.85	44.66 �� 29.85
March - May 2013 (HKLR03 Impact)	7.75 �� 3.96	24.23 �� 18.05
March - May 2014 (HKLR03 Impact)	6.51 �� 3.34	19.14 �� 7.19
March - May 2015 (HKLR03 Impact)	0.47 �� 0.73	2.36 �� 4.07
March - May 2016 (HKLR03 Impact)	0.98 �� 1.10	4.78 �� 6.85
March - May 2017 (HKLR03 Impact)	0.93 �� 1.03	5.25 �� 9.53
March - May 2018 (HKLR03 Impact)	2.88 �� 4.81	11.12 �� 22.46
March - May 2019 (HKLR03 Impact)	1.13 �� 1.39	2.54 �� 3.00
March - May 2020 (HKLR03 Impact)	0.56 �� 0.86	0.56 �� 0.86
March - May 2021 (TMCLKL Post-Construction)	1.13 �� 1.37	3.44 �� 4.26
March - May 2022 (TMCLKL Post-Construction)	0.00	0.00
March - May 2023 (HKLR03 Impact)	0.55 �� 0.86	1.35 �� 2.56
March - May 2024 (HKLR03 Impact)	0.57 �� 0.89	1.14 �� 1.77
March - May 2025 (HKLR03 Impact)	0.00	0.00

3.5.18 On review of the past 12 years' March-May quarterly periods (2013-2024), both STG and ANI have markedly decreased since 2015 (Table 3.7). As yet, there is no evidence that dolphins are returning to NWL, noting that HKLR03 marine works are still ongoing but will soon be completed. This quarter's findings are consistent with the data presented in the AFCD long-term monitoring report which records only two sightings in the past year April 2023-March 2024 (in September 2023 and January 2024) in the NWL area.

3.5.19 A two-way ANOVA with repeated measures and unequal sample sizes was conducted to examine whether there was a significant difference in average encounter rates between baseline and impact monitoring periods. The two variables that were examined included the two periods (baseline and impact phases) and two locations (NEL and NWL).

3.5.20 To compare the baseline period and the present quarter (40th quarter of the impact phase), the p-values for the differences in average dolphin encounter rates of STG and ANI were both 0.000000. If the alpha value is set at 0.000001, significant differences were still detected between the baseline and present quarter, in both the average dolphin encounter rates of STG and ANI.

3.5.21 To compare the baseline monitoring and all quarterly impact phase monitoring periods (i.e., 50 quarterly periods of the HKLR03/TMCLKL project), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.000000 and 0.000000, respectively. If the alpha value is set at 0.000001, significant differences were still detected between the baseline and present quarter, in both the average dolphin encounter rates of STG and ANI

3.5.22 As evidenced from encounter rate calculations, dolphin usage was markedly reduced in both NEL and NWL survey areas during the present quarterly period, when compared to the baseline period. A reduced occurrence of dolphins has been documented throughout the overall HZMB construction period.

3.5.23 The decline in the dolphin's use of both NEL and NWL is ongoing as are construction works for HZMB-related projects and other developments (Hung 2018). There is no indication that dolphins are returning to northern Lantau waters, however, HKLR03 construction works are still ongoing. It is noted that the Brothers Marine Park was established in 2016 to compensate for the permanent habitat loss that occurred during HZMB-related reclamation works.

Conclusion

3.5.24 During the present quarter of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White dolphins was noticeable from general observations.

3.5.25 Dolphins occurred infrequently in the NEL area immediately prior to the commencement of this project, including during the baseline monitoring period. There has been a declining use of the NEL area by dolphins since at least the late 1990's and many known individuals from the Brothers Islands habitat have re-located to other areas of Lantau Island or have not been recorded in Hong Kong waters.

3.5.26 As the EIA predicted that dolphins will return to northern Lantau waters following the completion of construction work, it is critical to keep monitoring both the NEL and NWL areas to continuously document how the dolphin��s habitat use is impacted by changes in construction activities, related to HZMB and other projects, and to assess if further mitigation measures can be applied.

3.6 Mudflat Monitoring Results

Sedimentation Rate Monitoring

3.6.1 The baseline sedimentation rate monitoring was in September 2012 and impact sedimentation rate monitoring was undertaken on 28 March 2025. The mudflat surface levels at the four established monitoring stations and the corresponding XYZ HK1980 GRID coordinates are presented in Table 3.8 and Table 3.9.

Table 3.8 Measured Mudflat Surface Level Results

	Baseline Monitoring (September 2012)			Impact Monitoring (March 2025)
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Easting (m)	Northing (m)	Surface Level (mPD)
S1	810291.160	816678.727	0.950	810291.150	816678.678	1.082
S2	810958.272	815831.531	0.864	810958.288	815831.534	0.959
S3	810716.585	815953.308	1.341	810716.575	815953.306	1.456
S4	811221.433	816151.381	0.931	811221.450	816151.390	1.121

Table 3.9 Comparison of Measurement

	Comparison of Measurement			Remarks and Recommendation
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Remarks and Recommendation
S1	-0.010	-0.049	0.132	Level continuously increased, need attention
S2	0.016	0.003	0.095	Level continuously increased, need attention
S3	-0.010	-0.002	0.115	Level continuously increased, need attention
S4	0.017	0.009	0.190	Level continuously increased, need attention

3.6.2 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased.

Water Quality Monitoring

3.6.3 The mudflat monitoring covered water quality monitoring data. Reference was made to the water quality monitoring data of the representative water quality monitoring station (i.e. SR3(N)) as in the EM&A Manual. The water quality monitoring location (SR3(N)) is shown in Figure 2.1)

3.6.4 Water quality monitoring in San Tau (monitoring station SR3(N)) was conducted in March 2025 as part of mudflat monitoring. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS).

3.6.5 The water monitoring result for SR3(N) were extracted and summarised in Table 3.10:

Table 3.10 Impact Water Quality Monitoring Results (Depth Average) at Station SR3(N)

	Mid Ebb Tide			Mid Flood Tide
	DO (mg/L)	Turbidity (NTU)	SS (mg/L)	DO (mg/L)	Turbidity (NTU)	SS (mg/L)
3 Mar 2025	6.7	2.8	12.1	6.3	2.8	16.9
5 Mar 2025	6.6	2.8	4.0	6.2	2.6	4.2
7 Mar 2025	5.8	3.4	3.3	5.9	3.5	3.3
10 Mar 2025	6.2	2.3	3.1	6.6	2.4	5.2
12 Mar 2025	6.8	2.7	2.9	6.6	2.3	2.7
14 Mar 2025	6.6	2.7	3.7	6.2	2.4	3.3
17 Mar 2025	6.9	3.1	5.2	6.5	2.7	4.9
19 Mar 2025	6.3	3.2	2.8	6.1	2.9	2.7
21 Mar 2025	6.6	3.1	5.1	6.3	2.8	5.2
24 Mar 2025	6.5	3.1	2.2	6.1	2.9	1.9
26 Mar 2025	6.1	3.3	3.8	6.0	3.3	3.1
28 Mar 2025	6.0	3.4	3.3	6.2	3.3	3.3
31 Mar 2025	6.1	3.3	2.4	6.0	3.2	2.6
Average	6.4	3.0	4.1	6.2	2.8	4.5

Mudflat Ecology Monitoring

Sampling Zone

3.6.6 To collect baseline information of mudflats in the study site, the study site was divided into three sampling zones (labeled as TC1, TC2, TC3) in Tung Chung Bay and one zone in San Tau (labeled as ST) (Figure 2.1 of Appendix O). The horizontal shoreline of sampling zones TC1, TC2, TC3 and ST were about 250 m, 300 m, 300 m and 250 m, respectively (Figure 2.2 of Appendix O). Survey of horseshoe crabs, seagrass beds and intertidal communities were conducted in every sampling zone. The present survey was conducted in March 2025 (totally 3 sampling days 1^st (for ST), 2^nd (for TC3), 3^rd (for TC2 and TC1).

3.6.7 Since the field survey of June 2016, increasing number of trashes and even big trashes (Figure 2.3 of Appendix O) were found in every sampling zone. It raised a concern about the solid waste dumping and current-driven waste issues in Tung Chung Wan. Respective measures (e.g., manual clean-up) should be implemented by responsible governmental agency units.

Horseshoe Crabs

3.6.8 Active search method was adopted for horseshoe crab monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any horseshoe crab individuals within 2-3 hour of low tide period (tidal level below 1.2 m above Chart Datum (C.D.)). Once a horseshoe crab individual was found, the species was identified referencing to Li (2008). The prosomal width, inhabiting substratum and respective GPS coordinate were recorded. A photographic record was taken for future investigation. Any grouping behavior of individuals, if found, was recorded.

3.6.9 In June 2017, a big horseshoe crab was tangled by a trash gill net in ST mudflat (Figure 2.3 of Appendix O). It was released to sea once after photo recording. The horseshoe crab of such size should be inhabiting sub-tidal environment while it forages on intertidal shore occasionally during high tide period. If it is tangled by the trash net for few days, it may die due to starvation or overheat during low tide period. These trash gill nets are definitely ��fatal trap�� for the horseshoe crabs and other marine life. Manual clean-up should be implemented as soon as possible by responsible governmental agency units.

Seagrass Beds

3.6.10 Active search method was adopted for seagrass bed monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any seagrass beds within 2-3 hours of low tide period. Once seagrass bed was found, the species, estimated area, estimated coverage percentage and respective GPS coordinates were recorded.

Intertidal Soft Shore Communities

3.6.11 The intertidal soft shore community surveys were conducted in low tide period. In every sampling zone, three 100m horizontal transect lines were laid at high tidal level (H: 2.0m above C.D.), mid tidal level (M: 1.5m above C.D.) and low tidal level (L: 1.0m above C.D.). Along every horizontal transect line, ten random quadrats (0.5 m x 0.5m) were placed.

3.6.12 Inside a quadrat, any visible epifauna was collected and was in-situ identified to the lowest practical taxonomical resolution. Whenever possible a hand core sample (10 cm internal diameter ´ 20 cm depth) of sediments was collected in the quadrat. The core sample was gently washed through a sieve of mesh size 2.0 mm in-situ. Any visible infauna was collected and identified. Finally, the top 5 cm surface sediment was dug for visible infauna in the quadrat regardless of hand core sample was taken.

3.6.13 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.

3.6.14 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

Data Analysis

3.6.15 Data collected from direct counting and core sampling was pooled in every quadrat for data analysis. Shannon-Weaver Diversity Index (H��) and Pielou��s Species Evenness (J) were calculated for every quadrat using the formulae below,

H��= -�U ( Ni / N ) ln ( Ni / N )(Shannon and Weaver, 1963)

J = H�� / ln S (Pielou, 1966)

where S is the total number of species in the sample, N is the total number of individuals, and Ni is the number of individuals of the i^th species.

Mudflat Ecology Monitoring Results and Conclusion

Horseshoe Crabs

3.6.16 Four juvenile horseshoe crabs and no adult were recorded in present surveys. Photo records of previously and currently observed horseshoe crabs are shown in Figure 3.1 of Appendix O and Figure 3.4 of Appendix O. The present survey results regarding horseshoe crabs are presented in Table 3.1 of Appendix O. The complete survey records are presented in Annex II of Appendix O.

3.6.17 In the survey of March 2015, there was one important finding that a mating pair of Carcinoscorpius rotundicauda was found in ST (prosomal width: male 155.1mm, female 138.2mm). It indicated the importance of ST as a breeding ground of horseshoe crab. In June 2017, mating pairs of Carcinoscorpius rotundicauda were found in TC2 (male 175.27 mm, female 143.51 mm) and TC3 (male 182.08 mm, female 145.63 mm) (Figure 3.2 of Appendix O). In December 2017 and June 2018, one mating pair was of Carcinoscorpius rotundicauda was found in TC3 (December 2017: male 127.80 mm, female 144.61 mm; June 2018: male 139 mm, female 149 mm). In June 2019, two mating pairs of Tachypleus tridentatus with large body sizes (male 150mm and Female 200mm; Male 180mm and Female 220mm) were found in TC3. Another mating pair of Tachypleus tridentatus was found in ST (male 140mm and Female 180mm). In March 2020, a pair of Tachypleus tridentatus with large body sizes (male 123mm and Female 137mm was recorded in TC1. Figure 3.2 of Appendix O shows the photographic records of the mating pair found. The recorded mating pairs were found nearly burrowing in soft mud at low tidal level (0.5-1.0 m above C.D.). The smaller male was holding the opisthosoma (abdomen carapace) of larger female from behind. A mating pair was found in TC1 in March 2020, it indicated that breeding of horseshoe crab could be possible along the coast of Tung Chung Wan rather than ST only, as long as suitable substratum was available. Based on the frequency of encounter, the shoreline between TC3 and ST should be more suitable mating ground. Moreover, suitable breeding period was believed in wet season (March �V September) because tiny individuals (i.e. newly hatched) were usually recorded in June and September every year (Figure 3.3 of Appendix O). One mating pair was found in June 2022. 3 adult individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda were recorded in September 2022 survey, with one alive, one dead in TC3 and one dead in TC2. June 2022, 7 large individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda was recorded (prosomal width ranged 131.4mm - 140.3mm) in TC3. In December 2018, one large individual of Carcinoscorpius rotundicauda was found in TC3 (prosomal width 148.9 mm). In March 2019, 3 large individuals (prosomal width ranged 220 �V 310mm) of Carcinoscorpius rotundicauda were observed in TC2. In June 2019, there were 3 and 7 large individuals of Tachypleus tridentatus recorded in ST (prosomal width ranged 140 �V 180mm) and TC3 (prosomal width ranged 150 �V 220mm), respectively. In March 2020, a mating pair of Tachypleus tridentatus was recorded in TC1 with prosomal width 123 mm and 137mm. Base on their sizes, it indicated that individuals of prosomal width larger than 100 mm would progress its nursery stage from intertidal habitat to sub-tidal habitat of Tung Chung Wan. The photo records of the large horseshoe crab are shown in Figure 3.4 of Appendix O. A dead specimen of adult horseshoe crab was seen at TC3 in March 2025 (Figure 3.4 (Cont��d) of Appendix O). These large individuals might move onto the intertidal shore occasionally during high tide for foraging and breeding. Because they should be inhabiting sub-tidal habitat most of the time. Their records were excluded from the data analysis to avoid mixing up with juvenile population living on intertidal habitat.

3.6.18 Some marked individuals were found in the previous surveys of September 2013, March 2014, and September 2014. All of them were released through a conservation programme in charged by Prof. Paul Shin (Department of Biology and Chemistry, The City University of Hong Kong (CityU)). It was a re-introduction trial of artificial bred horseshoe crab juvenile at selected sites. So that the horseshoe crab��s population might be restored in the natural habitat. Through a personal conversation with Prof. Shin, about 100 individuals were released in the sampling zone ST on 20 June 2013. All of them were marked with color tape and internal chip detected by specific chip sensor. There should be second round of release between June and September 2014 since new marked individuals were found in the survey of September 2014.

3.6.19 The artificial bred individuals, if found, would be excluded from the results of present monitoring programme in order to reflect the changes of natural population. However, the mark on their prosoma might have been detached during moulting after a certain period of release. The artificially released individuals were no longer distinguishable from the natural population without the specific chip sensor. The survey data collected would possibly cover both natural population and artificially bred individuals.

Population difference among the sampling zones

3.6.20 Figure 3.5 and 3.6 of Appendix O show the changes of number of individuals, meaning prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus in respectively in each sampling zone throughout the monitoring period.

3.6.21 To consider the entire monitoring period for TC3 and ST, medium to high search records (i.e. number of individuals) of both species (Carcinoscorpius rotundicauda and Tachypleus tridentatus) were usually found in wet season (June and September). The search record of ST was higher from September 2012 to June 2014 while it was replaced by TC3 from September 2014 to June 2015. The search records were similar between two sampling zones from September 2015 to June 2016. In September 2016, the search record of Carcinoscorpius rotundicauda in ST was much higher than TC3. From March to June 2017, the search records of both species were similar again between two sampling zones. It showed a natural variation of horseshoe crab population in these two zones due to weather condition and tidal effect. No obvious difference of horseshoe crab population was noted between TC3 and ST. In September 2017, the search records of both horseshoe crab species decreased except the Carcinoscorpius rotundicauda in TC3. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that the serial cyclone hit decreased horseshoe crab activity (totally 4 cyclone records between June and September 2017, to be discussed in 'Seagrass survey' section). From December 2017 to September 2018, the search records of both species increased again to low-moderate level in ST and TC3. From December 2018 to September 2019, the search records of Carcinoscorpius rotundicauda change from very low to low while the change of Tachypleus tridentatus was similar during this period. Relatively higher population fluctuation of Carcinoscorpius rotundicauda was observed in TC3. From March 2020 to September 2020, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were increased to moderate level in ST. However, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were decreased from very low to none in TC3 in this period. From March 2021 to September 2021, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were kept at low-moderate level in both ST and TC3. It is like the previous findings of June. It shows another growing phenomenon of horseshoe crabs, and it may be due to the weather variation of the start of wet season. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that September of 2021 was one of the hottest months in Hong Kong in record. As such, hot and shiny weather decreased horseshoe crab activity. In December 2021, no juvenile was recorded like previous in December due to the season. In March 2022, only juveniles recorded in both ST and TC3, no adult specimen was observed. In June 2022, total of 13 individuals of Carcinoscorpius rotundicauda and Tachypleus tridentatus were found, with 6 juveniles, 6 adults and 1 died recorded. In September 2022, total of 7 individuals of were found, with 4 juveniles, 3 adults (1 alive and 2 died) recorded. In March 2023, a total of 12 individuals of juveniles Carcinoscorpius rotundicauda and Tachypleus tridentatus were found and recorded. In June 2023, a total of 27 individuals of juveniles Tachypleus tridentatus were found and recorded. In September 2023, a total of 2 individuals of juveniles Tachypleus tridentatus were found and recorded. In December 2023, no horseshoe crab was found. In March and September 2024, Tachypleus tridentatus were found for each month. In December 2024, 2 individuals of juveniles Carcinoscorpius rotundicauda were found. Four individuals of juveniles Tachypleus tridentatus were recorded in March 2025.

3.6.22 For TC1, the search record was at a low to moderate level throughout the monitoring period. The change of Carcinoscorpius rotundicauda was relatively more variable than that of Tachypleus tridentatus. Relatively, the search record was very low in TC2. There were occasional records of 1 to 4 individuals between March and September throughout the monitoring period. The maximum record was 6 individuals only in June 2016.

3.6.23 About the body size, larger individuals of Carcinoscorpius rotundicauda were usually found in ST and TC1 relative to that in TC3 from September 2012 to June 2017. But the body size was higher in TC3 and ST followed by TC1 from September 2017 to March 2020. From June 2020 to December 2020, there was no individuals of Carcinoscorpius rotundicauda recorded in TC3 but in ST. The body size of Carcinoscorpius rotundicauda in ST was recorded gradually increased (from mean prosomal width 23.6mm to 49.6mm) since March 2020 to September 2020. From December 2020 to March 2021, the body size of Carcinoscorpius rotundicauda in ST was recorded decreased (from mean prosomal width 49.6mm to 43.3mm). In March 2021, the body size of Carcinoscorpius rotundicauda in TC3 (mean prosomal width 46.2mm) was recorded larger than that in ST (mean prosomal width 43.3mm). From September 2021 to June 2022, the body size of Carcinoscorpius rotundicauda in ST was recorded increased (from mean prosomal width 39.8mm to 54.42mm). For Tachypleus tridentatus, larger individuals were usually found in ST and TC3 followed by TC1 throughout the monitoring period. In June 2019, all found horseshoe crabs were large individuals and mating pairs. It is believed that the sizes of horseshoe crabs would decrease and gradually rise afterward due to the stable growth of juveniles after the spawning season. From March 2019 to September 2021, Tachypleus tridentatus were only recorded in TC3 and ST. The body size in TC3 increased from September 2019 to December 2019 then decreased in March 2020 and no recorded species in TC3 for three consecutive quarters from June 2020 to December 2020. From March 2020 to Sep 2021, the body size of Tachypleus tridentatus in TC3 increased (from mean prosomal width 34.00mm to 38.8mm). It showed a natural variation of horseshoe crab population in TC3. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. The body size in ST was gradually growth since December 2019 to September 2020 then slightly dropped in December 2020. In June 2022, T. tridentatus were only recorded in ST, the body size in ST decreased from mean prosomal width 77.59mm to 54.02mm in March 2022. In September 2022 T. tridentatus were only recorded in TC3. The mean prosomal was 61.09mm. In March 2023, 7 T. tridentatus were recorded in ST and TC3. The mean prosomal was 62.68mm. In March 2024, 2 T. tridentatus were recorded in ST with a mean prosomal width 70.55mm. No horseshoe crab was recorded in all sites in June 2024, and 2 T. tridentatus were recorded in ST with a mean prosomal width 40.00mm. In December 2024 2 Carcinoscorpius rotundicauda recorded with a mean prosomal width 43.00mm. In March 2025, 3 T. tridentatus were recorded in ST and 1 recorded at TC3.

3.6.24 In general, it was obvious that the shoreline along TC3 and ST (western shore of Tung Chung Wan) was an important nursery ground for horseshoe crab especially newly hatched individuals due to larger area of suitable substratum (fine sand or soft mud) and less human disturbance (far from urban district). Relatively, other sampling zones were not a suitable nursery ground, especially TC2. Possible factors were less area of suitable substratum (especially TC1) and higher human disturbance (TC1 and TC2: close to urban district and easily accessible). In TC2, large daily salinity fluctuation was a possible factor since it was flushed by two rivers under tidal inundation. The individuals inhabiting TC1 and TC2 were confined in small foraging area due to limited area of suitable substratum. Although there were mating pairs seldomly found in TC1 and TC2, the hatching rate and survival rate of newly hatched individuals were believed to be very low.

Seasonal variation of horseshoe crab population

3.6.25 Throughout the monitoring period, the search records of horseshoe crabs were fluctuated and at moderate �V very low level in June (Figure 3.5 and 3.6 of Appendix O). Low �V Very low search record was found in June 2013, totally 82 individuals of Tachypleus tridentatus and 0 ind. of Carcinoscorpius rotundicauda were found in TC1, TC3 and ST. Compare with the search record of June 2013, the numbers of Tachypleus tridentatus were gradually decreased in June 2014 and 2015 (55 ind. in 2014 and 18 ind. in 2015); the number of Carcinoscorpius rotundicauda raise to 88 and 66 ind. in June 2014 and 2015 respectively. In June 2016, the search record increased about 3 times compare with June 2015. In total, 182 individuals of Carcinoscorpius rotundicauda and 47 individuals of Tachypleus tridentatus were noted, respectively. Then, the search record was similar to June 2016. The number of recorded Carcinoscorpius rotundicauda (133 ind.) slightly dropped in June 2017. However, that of Tachypleus tridentatus rapidly increased (125 ind.). In June 2018, the search record was low to moderate while the numbers of Tachypleus tridentatus dropped sharply (39 ind.). In June 2019, 10 individuals of Tachypleus tridentatus were observed in TC3 and ST. All of them, however, were large individuals (prosomal width >100mm), their records are excluded from the data analysis to avoid mixing up with the juvenile population living on intertidal habitat. Until September 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually increased to 39 ind. and 28 ind., respectively. In December 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus greatly decreased to 3 ind. and 7 ind., respectively. In March 2022, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually decreased to 7 ind. and 2 ind., respectively in comparing with the March of previous record. The drop of abundance may be related to the unusual cold weather in the beginning of March 2022. Throughout the monitoring period, similar distribution of horseshoe crab population was found.

3.6.26 The search record of horseshoe crab declined obviously in all sampling zones during dry season especially December (Figure 3.5 and 3.6 of Appendix O) throughout the monitoring period. Very low �V low search record was found in December from 2012 to 2015 (0-4 ind. of Carcinoscorpius rotundicauda and 0 �V 12 ind. of Tachypleus tridentatus). The horseshoe crabs were inactive and burrowed in the sediments during cold weather (<15 ºC). Similar results of low search record in dry season were reported in a previous territory-wide survey of horseshoe crab. For example, the search records in Tung Chung Wan were 0.17 ind. hr^-1person^-1 and 0.00 ind. hr^-1 person^-1 in wet season and dry season respectively (details see Li, 2008). Compare with the search record of December from 2012 to 2015, which of December 2016 were much higher relatively. There were totally 70 individuals of Carcinoscorpius rotundicauda and 24 individuals of Tachypleus tridentatus in TC3 and ST. Since the survey was carried in earlier December with warm and sunny weather (~22 ºC during dawn according to Hong Kong Observatory database, Chek Lap Kok station on 5 December 2016), the horseshoe crab was more active (i.e. move onto intertidal shore during high tide for foraging and breeding) and easier to be found. In contrast, there was no search record in TC1 and TC2 because the survey was conducted in mid December with colder and cloudy weather (~20�XC during dawn on 19 December). The horseshoe crab activity would decrease gradually with the colder climate. In December of 2017, 2018 and 2019, very low search records were found again as mentioned above. No record of houseshoe crab was recorded in December 2022 and 2023.

3.6.27 From September 2012 to December 2013, Carcinoscorpius rotundicauda was less common species relative to Tachypleus tridentatus. Only 4 individuals were ever recorded in ST in December 2012. This species had ever been believed of very low density in ST hence the encounter rate was very low. In March 2014, it was found in all sampling zones with higher abundance in ST. Based on its average size (mean prosomal width 39.28 �V 49.81 mm), it indicated that breeding and spawning of this species had occurred about 3 years ago along the coastline of Tung Chun Wan. However, these individuals were still small while their walking trails were inconspicuous. Hence there was no search record in previous sampling months. Since March 2014, more individuals were recorded due to larger size and higher activity (i.e. more conspicuous walking trail).

3.6.28 For Tachypleus tridentatus, sharp increase of number of individuals was recorded in ST during the wet season of 2013 (from March to September). According to a personal conversation with Prof. Shin (CityU), his monitoring team had recorded similar increase of horseshoe crab population during wet season. It was believed that the suitable ambient temperature increased its conspicuousness. However similar pattern was not recorded in the following wet seasons. The number of individuals increased in March and June 2014 and followed by a rapid decline in September 2014. Then the number of individuals fluctuated slightly in TC3 and ST until March 2017. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. Since the mean prosomal width of Tachypleus tridentatus continued to grow and reached about 50 mm since March 2014. Then it varied slightly between 35-65 mm from September 2014 to March 2017.Most of the individuals might have reached a suitable size (e.g. prosomal width 50 �V 60 mm) strong enough to forage in sub-tidal habitat. In June 2017, the number of individuals increased sharply again in TC3 and ST. Although mating pair of Tachypleus tridentatus was not found in previous surveys, there should be new round of spawning in the wet season of 2016. The individuals might have grown to a more conspicuous size in 2017 accounting for higher search record. In September 2017, moderate numbers of individual were found in TC3 and ST indicating a stable population size. From September 2018 to March 2020, the population size was low while natural mortality was the possible cause. From June 2020 to September 2020, the population size of Tachypleus tridentatus increased to moderate level in ST while the mean proposal width of them conitued to grow and reach about 55mm. The population size of Tachypleus tridentatus slightly decreased in ST from March 2021 to March 2022 and the mean proposal width of them increased to about 77.59mm.

3.6.29 In recent year, the Carcinoscorpius rotundicauda was a more common horseshoe crab species in Tung Chung Wan. It was recorded in the four sampling zones while the majority of population located in TC3 and ST. Due to potential breeding last year, the number of Tachypleus tridentatus increased in ST. Since TC3 and ST were regarded as important nursery ground for both horseshoe crab species, box plots of prosomal width of two horseshoe crab species were constructed to investigate the changes of population in details.

Box plot of horseshoe crab populations in TC3

3.6.30 Figure 3.7 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in ST. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. From March 2014 to September 2018, the size of major population decreased, and more small individuals (i.e. lower whisker) were recorded after June of every year. It indicated a new round of spawning. Also, there were similar increasing trends of body size from September to June of next year between 2014 and 2017. It indicated a stable growth of individuals. The larger juveniles (i.e. upper whisker usually ranged 60 �V 80 mm in prosomal width except one individual (prosomal width 107.04 mm) found in March 2017. It reflected that juveniles reaching this size would gradually migrate to sub-tidal habitats.

3.6.31 For Tachypleus tridentatus, the major size ranged 20-50 mm while the number of individuals fluctuated from September 2012 to June 2014. Then a slight but consistent growing trend was observed from September 2014 to June 2015. The prosomal width increased from 25 �V 35 mm to 35 �V 65 mm. As mentioned, the large individuals might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. It accounted for the declined population in TC3. From March to September 2016, slight increasing trend of major size was noticed again. From December 2016 to June 2017, similar increasing trend of major size was noted with much higher number of individuals. It reflected new round of spawning. In September 2017, the major size decreased while the trend was different from previous two years. Such decline might be the cause of serial cyclone hit between June and September 2017 (to be discussed in the 'Seagrass survey' section). From December 2017 to September 2018, increasing trend was noted again. It indicated a stable growth of individuals. From September 2018 to that of next year, the average prosomal widths were decreased from 60mm to 36mm. It indicated new rounds of spawning occurred during September to November 2018. In December 2019, an individual with larger body size (prosomal width 65mm) was found in TC3 which reflected the stable growth of individuals. In March 2020, the average prosomal width (middle line of the whole box) of Tachypleus tridentatus in TC3 was 33.97mm which is smaller than that in December 2019. It was in normal fluctuation. From June 2020 to December 2020, no horseshoe crab was recorded in TC3. In Sep 2021, only one Tachypleus tridentatus with body size (prosomal width 38.78mm) was found in TC3. The decrease in the species population was considered to be related to hot weather in September, which may affect their activity. Across the whole monitoring period, the larger juveniles (upper whisker) usually reached 60 �V 80 mm in prosomal width, even 90 mm occasionally. The juveniles reaching this size might gradually migrate to sub-tidal habitats.

Box plot of horseshoe crab populations in ST

3.6.32 Figure 3.8 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in ST. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. From March 2014 to September 2018, the size of major population decreased and more small individuals (i.e. lower whisker) were recorded after June of every year. It indicated new round of spawning. Also there were similar increasing trends of body size from September to June of next year between 2014 and 2017. It indicated a stable growth of individuals. The larger juveniles (i.e. upper whisker usually ranged 60 �V 80 mm in prosomal width except one individual (prosomal width 107.04 mm) found in March 2017. It reflected juveniles reaching this size would gradually migrate to sub-tidal habitats.

3.6.33 For Tachypleus tridentatus, a consistent growing trend was observed for the major population from December 2012 to December 2014 regardless of change of search record. The prosomal width increased from 15 �V 30 mm to 60 �V 70 mm. As mentioned, the large juveniles might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. From March to September 2015, the size of major population decreased slightly to a prosomal width 40 �V 60 mm. At the same time, the number of individuals decreased gradually. It further indicated some of large juveniles might have migrated to sub-tidal habitat, leaving the smaller individuals on shore. There was an overall growth trend. In December 2015, two big individuals (prosomal width 89.27 mm and 98.89 mm) were recorded only while it could not represent the major population. In March 2016, the number of individual was very few in ST that no box plot could be produced. In June 2016, the prosomal width of major population ranged 50 �V 70 mm. But it dropped clearly to 30 �V 40 mm in September 2016 followed by an increase to 40 �V 50 mm in December 2016, 40 �V 70 mm in March 2017 and 50 �V 60mm in June 2017. Based on overall higher number of small individuals from June 2016 to September 2017, it indicated another round of spawning. From September 2017 to June 2018, the major size range increased slightly from 40 �V 50 mm to 45 �V 60 mm indicating a continuous growth. In September 2018, decrease of major size was noted again that might reflect new round of spawning. Throughout the monitoring period, the larger juveniles ranged 60-80 mm in prosomal width. Juveniles reaching this size would gradually migrate to sub-tidal habitats.

3.6.34 As a summary for horseshoe crab populations in TC3 and ST, there were spawning ground of Carcinoscorpius rotundicauda from 2014 to 2018 while the spawning time should be in spring. The population size was consistent in these two sampling zones. For Tachypleus tridentatus, small individuals were rarely found in both zones from 2014 to 2015. It was believed no occurrence of successful spawning. The existing individuals (that recorded since 2012) grew to a mature size and migrated to sub-tidal habitat. Hence the number of individuals decreased gradually. From 2016 to 2018, new rounds of spawning were recorded in ST while the population size increased to a moderate level.

3.6.35 In March 2019 to June 2019 and Dec 2021, no horseshoe crab juveniles (prosomal width <100mm) were recorded in TC3 and ST. All recorded horseshoe crabs were large individuals (prosomal width >100mm) or mating pairs which were all excluded from the data analysis. From September 2019 to September 2020, the population size of both horseshoe crab species in ST gradually increased to moderate level while their body sizes were mostly in small to medium range (~23 �V 55mm). It indicated the natural stable growth of the horseshoe crab juveniles. In December 2020, the population size of both horseshoe crab species in ST dropped to low level while their body sizes were mostly in small to medium range (~28 �V 56mm). It showed the natural mortality and seasonal variation of horseshoe crab. In June 2022, the population size of both horseshoe crab species in ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~51�V78mm). In September 2022, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~56�V62mm). In September 2023, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~44-79mm).

Impact of the HKLR project

3.6.36 It was the 51^st survey of the EM&A programme during the construction period. Based on the monitoring results, no detectable impact on horseshoe crab was revealed due to HKLR project. The population change was mainly determined by seasonal variation, no abnormal phenomenon of horseshoe crab individual, such as large number of dead individuals on the shore had been reported.

Discussion

3.6.37 There are 4 juvenile horseshoe crabs recorded in March 2025. The population of horseshoe crabs recorded in recent years has been in a decreasing trend since 2021, referring to Figure 3.5 of Appendix O. It is noted that the inter-tidal habitat for the juvenile horseshoe crabs within the monitoring sites is become smaller in area due to increased seagrass colonization as indicated by seagrass monitoring results, i.e. seagrasses cover area increased in recent years (refer to Figure 3.11 of Appendix O). The juvenile horseshoe crabs prefer open soft mud/sand habitat as they can easily burrow in the mud/sand to hide themselves when the habitat exposed during low tide. When the mud/sand habitat was colonized by seagrasses, the roots of seagrasses made it difficult for horseshoe crab to burrow and hide. In this situation, horseshoe crabs may avoid habitat or being easily predated by predators such as birds. All seagrasses disappeared as observed during monitoring in December 2024, and one of the two seagrasses is observed in March 2025 re-generated at a small area along mangal edge. Attention will be given to subsequent monitoring, if it will affect the breeding activities of the horseshoe crabs

Seagrass Beds

3.6.38 All seagrasses were observed disappeared within monitoring areas of Tung Chung and San Tau during the last quarterly ecological monitoring in December 2024. However, one of the two seagrass species, i.e., Zostera japonica is re-generated during the survey in March 2025. It is likely that the underground roots of this seagrass maintained alive when the above ground plant part died during last season, i.e., December 2024. Zostera japonica was found only in ST. At close vicinity to mangrove, one small sized 25 square meter) of Zostera japonica beds were observed at tidal zone 2.0m above C.D in ST. The widely distributed seagrass, Halophila ovalis in recent years totally disappeared in December 2024 and did not observe re-generation in March 2025. Table 3.2 of Appendix O summarizes the results of the present seagrass beds survey, and the photograph records of the seagrass bed are shown in Figure 3.9 of Appendix O. The complete record throughout the monitoring period is presented in Annex III of Appendix O.

3.6.39 Since the commencement of the EM&A monitoring programme, two species of seagrass Halophila ovalis and Zostera japonica were recorded in TC3 and ST (Figure 3.10 of Appendix O). In general, Halophila ovalis was occasionally found in TC3 in few small to medium patches. But it was commonly found in ST in medium to large seagrass bed. Moreover, it had sometimes grown extensively and had covered significant mudflat area at 0.5 �V 2.0 m above C.D. between TC3 and ST. Another seagrass species Zostera japonica was found in ST only. It has restricted distribution in a few locations with small vegetation coverage, and it partially co-existed with Halophila ovalis near the edge of the mangrove strand at 2.0 m above C.D.

3.6.40 According to the previous results, majority of seagrass bed was confined in ST, while it increasingly established at TC3 in recent years, and the temporal change of both seagrass species was investigated in detail:

Temporal variation of seagrass beds in ST

3.6.41 Figure 3.11 of Appendix O shows the changes of estimated total area of seagrass beds in ST along the sampling months. For Zostera japonica, it was not recorded in the 1^st and 2^nd surveys of monitoring programme. Seasonal recruitment of few, small patches (total seagrass area: 10 m²) was found in March 2013 that grew within the large patch of seagrass Halophila ovalis. Then, the patch size increased and merged gradually with the warmer climate from March to June 2013 (15 m²). However, the patch size decreased and remained similar from September 2013 (4 m²) to March 2014 (3 m²). In June 2014, the patch size increased obviously again (41 m²) with warmer climate followed by a decrease between September 2014 (2 m²) and December 2014 (5 m²). From March to June 2015, the patch size increased sharply again (90 m²). It might be due to the disappearance of the originally dominant seagrass Halophila ovalis resulting in less competition for substratum and nutrients. From September 2015 to June 2016, it was found coexisting with seagrass Halophila ovalis with steady increasing patch size (from 44 m² to 115 m²) and variable coverage. In September 2016, the patch size decreased again to (38 m²) followed by an increase to a horizontal strand (105.4 m²) in June 2017. And it did no longer co-existed with Halophila ovalis. Between September 2014 and June 2017, an increasing trend was noticed from September to June of next year followed by a rapid decline in September of next year. It was possibly the cause of heat stress, typhoon and stronger grazing pressure during the wet season. However, such increasing trend was not found from September 2017 to March 2021, while no patch of Zostera japonica was found. From June 2021, the species was recorded again with a coverage of 45m²in area. The recorded area of the seagrass bed in September 2021 survey was slightly decreased to 15m². The Z. japonica was consistently present at the monitoring site still September 2024, and it disappeared in December 2024.

3.6.42 For Halophila ovalis, it was recorded as 3 �V 4 media to large patches (area 18.9- 251.7 m²; vegetation coverage 50 �V 80%) beside the mangrove vegetation at tidal level 2 m above C.D. in September 2012. The total seagrass bed area grew steadily from 332.3 m² in September 2012 to 727.4 m² in December 2013. Flowers were observed in the largest patch during its flowering period. In March 2014, 31 small to medium patches were newly recorded (variable area 1 �V 72 m² per patch, vegetation coverage 40-80% per patch) in lower tidal zone between 1.0 and 1.5 m above C.D. The total seagrass area increased further to 1350 m². In June 2014, these small and medium patches grew and extended to each other. These patches were no longer distinguishable and were covering a significant mudflat area of ST. It was generally grouped into 4 large patches (1116 �V 2443 m²) of seagrass beds characterized of patchy distribution, variable vegetable coverage (40-80%) and smaller leaves. The total seagrass bed area increased sharply to 7629 m². In September 2014, the total seagrass area declined sharply to 1111m². There were only 3-4 small to large patches (6 �V 253 m²) at high tidal level and 1 large patch at low tidal level (786 m²). Typhoons or strong water current was a possible cause (Fong, 1998). In September 2014, there were two tropical cyclone records in Hong Kong (7^th �V 8^thSeptember: no cyclone name, maximum signal number 1; 14^th �V 17^thSeptember: Kalmaegi, maximum signal number 8SE) before the seagrass survey dated 21^stSeptember 2014. The strong water current caused by the cyclone Kalmaegi especially might have damaged the seagrass beds. In addition, natural heat stress and grazing force were other possible causes reducing seagrass beds area. Besides, very small patches of Halophila ovalis could be found in other mud flat areas in addition to the recorded patches. But it was hardly distinguished due to very low coverage (10 �V 20%) and small leaves.

3.6.43 In December 2014, all the seagrass patches of Halophila ovalis disappeared in ST. Figure 3.12 of Appendix O shows the difference of the original seagrass beds area nearby the mangrove vegetation at high tidal level between June 2014 and December 2014. Such rapid loss would not be seasonal phenomenon because the seagrass beds at higher tidal level (2.0 m above C.D.) were present and normal in December 2012 and 2013. According to Fong (1998), similar incident had occurred in ST in the past. The original seagrass area had declined significantly during the commencement of the construction and reclamation works for the international airport at Chek Lap Kok in 1992. The seagrass almost disappeared in 1995 and recovered gradually after the completion of reclamation works. Moreover, incident of rapid loss of seagrass area was also recorded in another intertidal mudflat in Lai Chi Wo in 1998 with unknown reason. Hence, Halophila ovalis was regarded as a short- lived and r- strategy seagrass that could colonize areas in short period but disappears quickly under unfavourable conditions (Fong, 1998).

Unfavourable conditions to seagrass Halophila ovalis

3.6.44 Typhoon or strong water current was suggested as one unfavorable condition to Halophila ovalis (Fong, 1998). As mentioned above, there were two tropical cyclone records in Hong Kong in September 2014. The strong water current caused by the cyclones might have given damage to the seagrass beds.

3.6.45 Prolonged light deprivation due to turbid water would be another unfavorable condition. Previous studies reported that Halophila ovalis had little tolerance to light deprivation. During experimental darkness, seagrass biomass declined rapidly after 3-6 days and seagrass died completely after 30 days. The rapid death might be due to shortage of available carbohydrate under limited photosynthesis or accumulation of phytotoxic end products of anaerobic respiration (details see Longstaff et al., 1999). Hence the seagrass bed of this species was susceptible to temporary light deprivation events such as flooding river runoff (Longstaff and Dennison, 1999).

3.6.46 In order to investigate any deterioration of water quality (e.g. more turbid) in ST, the water quality measurement results at two closest monitoring stations SR3 and IS5 of the EM&A programme were obtained from the water quality monitoring team. Based on the results from June to December 2014, the overall water quality was in normal fluctuation except there was one exceedance of suspended solids (SS) at both stations in September. On 10^th September 2014, the SS concentrations measured during mid-ebb tide at stations SR3 (27.5 mg/L) and IS5 (34.5 mg/L) exceeded the Action Level (≤ 23.5 mg/L and 120% of upstream control station��s reading) and Limit Level (≤ 34.4 mg/L and 130% of upstream control station��s reading) respectively. The turbidity readings at SR3 and IS5 reached 24.8 �V 25.3 NTU and 22.3 �V 22.5 NTU, respectively. The temporary turbid water should not be caused by the runoff from upstream rivers. Because there was no rain or slight rain from 1^st to 10^th September 2014 (daily total rainfall at the Hong Kong International Airport: 0 �V 2.1 mm; extracted from the climatological data of Hong Kong Observatory). The effect of upstream runoff on water quality should be neglectable in that period. Moreover the exceedance of water quality was considered unlikely to be related to the contract works of HKLR according to the ��Notifications of Environmental Quality Limits Exceedances�� provided by the respective environmental team. The respective construction of seawall and stone column works, which possibly caused turbid water, was carried out within silt curtain as recommended in the EIA report. Moreover there was no leakage of turbid water, abnormity or malpractice recorded during water sampling. In general, the exceedance of suspended solids concentration was considered to be attributed to other external factors, rather than the contract works.

3.6.47 Based on the weather condition and water quality results in ST, the co-occurrence of cyclone hit and turbid waters in September 2014 might have combined the adverse effects on Halophila ovalis that leaded to disappearance of this short-lived and r-strategy seagrass species. Fortunately Halophila ovalis was a fast-growing species (Vermaat et al., 1995). Previous studies showed that the seagrass bed could be recovered to the original sizes in 2 months through vegetative propagation after experimental clearance (Supanwanid, 1996). Moreover it was reported to recover rapidly in less than 20 days after dugong herbivory (Nakaoka and Aioi, 1999). As mentioned, the disappeared seagrass in ST in 1995 could recover gradually after the completion of reclamation works for international airport (Fong, 1998). The seagrass beds of Halophila ovalis might recolonize in the mudflat of ST through seed reproduction as long as there was no unfavourable condition in the coming months.

Recolonization of seagrass beds

3.6.48 Figure 3.12 of Appendix O shows the recolonization of seagrass bed in ST from December 2014 to September 2024. From March to June 2015, 2 �V 3 small patches of Halophila ovalis were newly found co-inhabiting with another seagrass species Zostera japonica. But the total patch area of Halophila ovalis was still very low compared with previous records. The recolonization rate was low while cold weather and insufficient sunlight were possible factors between December 2014 and March 2015. Moreover, it would need to compete with seagrass Zostera japonica for substratum and nutrient, because Zostera japonica had extended and covered the original seagrass bed of Halophila ovalis at certain degree. From June 2015 to March 2016, the total seagrass area of Halophila ovalis had increased rapidly from 6.8 m² to 230.63 m². It had recolonized its original patch locations and covered its competitor Zostera japonica. In June 2016, the total seagrass area increased sharply to 4707.3m². Like the previous records of March to June 2014, the original patch area of Halophila ovalis increased further to a horizontally long strand. Another large seagrass beds colonized the lower tidal zone (1.0 �V 1.5 m above C.D.). In September 2016, this patch extended much and covered significant soft mud area of ST, resulting in sharp increase of total area (24245 m²). It indicated the second extensive colonization of this r-selected seagrass. In December 2016, this extensive seagrass patch decreased in size and had been separated into few, undistinguishable patches. Moreover, the horizontal strand nearby the mangrove vegetation decreased in size. The total seagrass bed decreased to 12550 m². From March to June 2017, the seagrass bed area remained generally stable (12438- 17046.5 m²) but the vegetation coverage fluctuated (20 �V 50% in March 2017 to 80 �V 100% in June 2017). The whole recolonization process took about 2.5 years.

Second disappearance of seagrass bed

3.6.49 In September 2017, the whole seagrass bed of Halophila ovalis disappeared again along the shore of TC3 and ST (Figure 3.12 of Appendix O). Like the first disappearance of seagrass bed occurred between September and December 2014, strong water current (e.g. cyclone) or deteriorated water qualities (e.g. high turbidity) was the possible cause.

3.6.50 Between the survey periods of June and September 2017, there were four tropical cyclone records in Hong Kong (Merbok in 12- 13^th, June; Roke in 23^rd, Jul.; Hato in22 �V 23^rd, Aug.; Pakhar in 26 �V 27^th, Aug.) (Online database of Hong Kong Observatory) All of them reached signal 8 or above, especially Hato with highest signal 10.

3.6.51 According to the water quality monitoring results (July to August 2017) of the two closest monitoring stations SR3 and IS5 of the respective EM&A programme, the overall water quality was in normal fluctuation. There was an exceedance of suspended solids (SS) at SR3 on 12 July 2017. The SS concentration reached 24.7 mg/L during mid-ebb tide, which exceeded the Action Level (≤ 23.5 mg/L). But it was far below the Limit Level (≤ 34.4 mg/L). Since such exceedance was slight and temporary, its effect to seagrass bed should be minimal.

3.6.52 Overall, the disappearance of seagrass beds in ST has believed the cause of serial cyclone hit in July and August 2017. Based on previous findings, the seagrass beds of both species were expected to recolonize in the mudflat if the vicinal water quality was normal. The whole recolonization process (from few, small patches to extensive strand) would gradually lasting at least 2 years. From December 2017 to March 2018, there was still no recolonization of few, small patches of seagrass at the usual location (Figure 3.12 of Appendix O). It was different from the previous round (March 2015 �V June 2017). Until June 2018, the new seagrass patches with small-medium size were found at the usual location (seaward side of mangrove plantation at 2.0 m C.D.) again, indicating the recolonization. However, the seagrass bed area decreased sharply to 22.5 m² in September 2018. Again it was believed that the decrease was due to the hit of the super cyclone in September 2018 (Mangkhuton 16^th September, highest signal 10). From December 2018 to June 2019, the seagrass bed area increased from 404 m² to 1229 m² while the vegetation coverage is also increased (December 2018: 5�V 85%; March 2019: 50 �V 100% and June 2019: 60 �V 100%). Relatively, the whole recolonization process would occur slower than the previous round (more than 2 years). From September 2019 to March 2021, the seagrass bed area in ST slightly decreased from 1200 m²to 942.05 m²,which were in normal fluctuation. From March 2021 to December 2021, the seagrass bed area in ST decreased from 942.05 m²to 680m²,which were in normal fluctuation. In March 2022, the seagrass bed area in ST increased significantly to approximately 2040 m^2,which believed to be related to more rain in current dry season. It was observed that the brown filamental algae bloom occurred at ST site in March 2022. Distribution of the algae was overlapped with seagrass beds, mainly the species Halophila ovalis and the algae was grown over the top of the seagrass. In some areas, the brown filamental algae fully covered the seagrass bed, referring to Figure 3.9. The seagrass was still alive when checked during the field survey. Whether the algae bloom will kill seagrass in longer period time is unknown. The seagrass distribution and health condition should be checked in the coming June monitoring. The algae bloom of the brown filamental algae at the seagrass bed disappeared as observed in June 2022, referring to Figure 3.9. Seagrass in December 2022 and September 2022 have decreased compared to June 2022 due to normal seasonal change. Seagrass in March 2023 have increased compare to previous quarter due to normal seasonal change. Seagrass in June 2023 have further increased around 20% compared to the previous period. Seagrass in September and December 2023 have decreased compared to previous quarter due to normal seasonal change. In March 2024, seagrass increased compared to the previous quarter. In September 2024, seagrass coverage increased compare to the previous quarter.

Third disappearance of seagrass bed

3.6.53 All seagrass beds were observed disappeared at the monitoring sites during the December monitoring event in 2024. There were two typhoon/cyclone events that occurred during November 2024 which was an unusual local weather condition, and it may cause the disappearance of the seagrasses.

Impact of the HKLR project

3.6.54 It was the 51^st survey of the EM&A Programme during the construction period. Throughout the monitoring period, the disappearance of seagrass beds in three occasions was believed to be the cause of cyclone hits rather than impact of HKLR project. The seagrass bed was recolonized since there had been a gradual increase in size and number from December 2018 to September 2024 after the hit of the super cyclone in September 2018. The seagrass bed area decreased from March 2021 to December 2021, which was in normal fluctuation. It is observed that the seagrass Halophila ovalis covered a larger area than before. Total seagrass bed area significantly increased from March 2022 to June 2022 and slightly reduced in September 2022. Seagrass in September and December 2023 have decreased compared to previous quarter and increased in March, June, and September 2024. The third time seagrass bed disappearance was observed during quarterly monitoring in December 2024 and one of the two seagrass species regenerated in March 2025 in ST.

Intertidal Soft Shore Communities

Substratum

3.6.55 Table 3.3 of Appendix O and Figure 3.13 of Appendix O show the substratum types along the horizontal transect at every tidal level in all sampling zones. The relative distribution of substratum types was estimated by categorizing the substratum types (Gravels & Boulders / Sands / Soft mud) of the ten random quadrats along the horizontal transect. The distribution of substratum types varied among tidal levels and sampling zones:

�P In TC1, high percentages of ��Gravels and Boulders�� (80%) were recorded at a high tidal level. At mid tidal level, Gravels and Boulders �� was the main substratum type (80%), following by ��Sands�� (15%) and ��Soft mud�� (5%). At low tidal level, ��Soft mud�� was the main substratum type (90%), followed by ��Sands�� (10%).

�P In TC2, the high percentages of ��Gravels and Boulders�� (90%) was recorded at high tidal level, following by ��Sands�� (10%). At mid tidal levels, Gravels and Boulders�� was the main substratum type (80%), following by ��Sands�� (10%) and ��Soft mud�� (10%). At low tidal level, ��Soft mud�� covered 95%, ��Gravels and Boulders�� and ��Sands �� covered the remaining 5% of the transect.

�P In TC3, the higher percentage of ��Gravels and Boulders�� was recorded at high tidal level (90%), following by ��Sands�� and Soft mud covered remaining 10%. At mid tidal level, ��Gravels and Boulders�� was the main substratum type (70%), following by ��Sands�� (15%) and ��Soft mud�� 15%). At low tidal level, ��Soft mud�� covered 90% of the transect, and ��Sands �� covered 5% and ��Gravels and Boulders�� covered 5% of the transect.

�P In ST, ��Gravels and Boulders�� was the main substratum type (90%) at high tidal level, followed by ��Sands�� (510). At mid tidal levels, Gravels and Boulders�� was the main substratum type (70%), following by ��Sands�� (15%) and ��Soft mud�� (15%). At low tidal level, ��Soft mud�� was the main substratum type (85%), ��Sands�� covered 10% of the transect, ��Gravels and Boulders�� covered 5% of the transect.

3.6.56 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.

Soft shore communities

3.6.57 Table 3.4 of Appendix O lists the total abundance, density and number of taxon of every phylum in this survey. A total of 7,580 individuals were recorded. Mollusca was the most abundant phylum (total abundance 6,633 ind., density 221 ind. m^-2, relative abundance 87.5%). The second and third were Arthropoda 559 ind., 19 ind. m^-2, 7.4%) which followed by Sipuncula (172 ind., 6 ind. m^-2, 2.3%) and Annelida (102 ind., 3 ind. m^-2, 1.3%), respectively. The fifth was Cnidania with total abundance 60 ind., density 2 ind.m^-2and relative abundance 0.8%. The sixth was Nemertea with total abundance 39 ind., density 1 ind.m^-2and relative abundance 0.5%. Platyhelminthes was very low in abundances (density 1 ind. m^-2, relative abundance 0.2%). Moreover, the most diverse phylum was Mollusca (32 taxa) followed by Arthropoda (6 taxa). Annelida (3 taxa) and Sipuncula (2 taxa). There was 1 taxon for Nemertea, Cnidaria and Platyhelminthes.

3.6.58 The taxonomic resolution and complete list of recorded fauna are shown in Appendix OV and V respectively. As reported in June 2018, taxonomic revision of three potamidid snail species was conducted according to the latest identification key published by Agriculture, Fisheries and Conservation Department (details see AFCD, 2018), the species names of following gastropod species were revised:

�P Cerithidea cingulata was revised as Pirenella asiatica

�P Cerithidea djadjariensis was revised as Pirenella incisa

�P Cerithidea rhizophorarum was revised as Cerithidea moerchii

Moreover, taxonomic revision was conducted on another snail species while the specie name was revised:

�P Batillaria bornii was revised as Clypeomorus bifasciata

3.6.59 In March 2021, an increased number of sea slugs and their eggs were observed in all sampling zones. It may due to the breeding season of sea slug and the increased of algae on the intertidal.

3.6.60 Table 3.5 of Appendix O shows the number of individuals, relative abundance and density of each phylum in every sampling zone. The total abundance (1,787 �V 2,009 ind.) varied among the four sampling zones while the phyla distributions were similar. In general, Mollusca was the most dominant phylum (no. of individuals: 1,548 �V 1,793 ind.; relative abundance 83.6% - 89.2%; density 206 - 239 ind. m^-2). Other phyla were much lower in number of individuals. Arthropoda (109 - 225 ind.; 5.4% �V 12.1%; 15 - 30 ind. m^-2) was common phyla relatively. Other phyla were very low in abundance in all sampling zones.

Dominant species in every sampling zone

3.6.61 Table 3.6 of Appendix O lists the abundant species in every sampling zone. In the present survey, most of the listed abundant species were of low to moderate densities (42 �V 95 ind. m^-2). Few of the listed species were of high or very high density (>100 ind. m^-2), which were regarded as dominant species. Other listed species of lower density (<42 ind. m^-2) were regarded as common species.

3.6.62 In TC1, the substratum was mainly ��Gravels and Boulders�� at high and mid tidal levels. At high tidal level, the rock oyster Saccostrea cucullata (mean density 109 ind. m^-2; relative abundance 39%) was the dominant species found at high density and the gastropod Monodonta labio (65 ind. m^-2; relative abundance 23%) was of low to moderate density. At mid tidal level, the rock oyster Saccostrea cucullata (80 ind. m^-2, 33%) was at dominant species with low to moderate density. The gastropod Monodonta labio (51 ind. m^-2, 21%) was at low to moderate densities, followed by Batillaria zonalis (36ind. M^-2, 15%) at low to moderate densities. At low tidal level (main substratum type ��Soft mud��), the Batillaria multiformis (44 ind. m^-2, 22%), the Nodilittorina radiata (39 ind. m^-2, 20%) and Barbatia virescens (32 ind. m^-2, 16%) were of lower density, regarded as common species.

3.6.63 In TC2, the substratum types were mainly ' Gravels and Boulders' at a high tidal level. The rock oyster Saccostrea cucullata (113 ind. m^-2, 38%) was the dominant species found at high density. The gastropod Monodonta labio (60 ind. m^-2, 20%) was dominant at low to moderate density and the Batillaria multiformis (38 ind. m^-2, 13%) was at lower density. At mid tidal level (main substratum types ��Soft mud�� and ��Gravels and Boulders��), rock oyster Saccostrea cucullata (79 ind. m^-2, 34%), gastropods Monodonta zonalis (32 ind. m^-2, 14%) and Batillaria labio (38 ind. m^-2, 16%) were dominant at low density. Substratum types ��Soft Mud�� were mainly distributed at low tidal level, the Barbatia virescens (54 ind. m^-2, 26%) was dominant at low densities, the Batillaria multiformis (40 ind. m^-2, 19%) were of lower densities, regarded as common species.

3.6.64 In TC3, the substratum type was mainly ��Gravels and Boulders�� at high tidal level. The rock oyster Saccostrea cucullata (117 ind. m^-2, 40%) was of dominant species at high density and the gastropod Monodonta labio (66 ind. m^-2, 22%) was of low to moderate density. At mid tidal level (main substratum types ��Gravels and Boulders��), the rock oyster Saccostrea cucullata (86 ind. m^-2, 35%) was of the dominant species at low to moderate density. The gastropod Monodonta labio (40 ind. m^-2, 17%) was at low density level. At low tidal level, the major substratum type was ��Soft mud��. The Barbatia virescens (51 ind. m^-2, 22%) at low to moderate density. The Lunella granulate (37 ind. m^-2, 16%), Batillaria multiformis (35 ind. m^-2, 15%) were dominant at low densities.

3.6.65 In ST, the major substratum type was ��Gravels and Boulders�� at high tidal level. At high tidal level, the rock oyster Saccostrea cucullata (110 ind. m^-2, 38%) was abundant at high density. The gastropods Monodonta labio(48 ind. m^-2, 16%) were at low to moderate densities. At mid tidal level (main substratum types ��Gravels and Boulders��), the gastropod Monodonta labio (100 ind. m^-2, 33%) was abundant at high density. The rock oyster Saccostrea cucullata (82 ind. m^-2, 27%) was the dominant species at low to moderate densities. At low tidal level (major substratum: ��Soft mud��), the Batillaria zonalis (61 ind. m^-2, 29%) was at low to moderate densities and Lunella granulata (39 ind. m^-2, 18%) was at low density.

3.6.66 In general, there was no consistent zonation pattern of species distribution across all sampling zones and tidal levels. The species distribution was determined by the type of substratum primarily. In general, rock oyster Saccostrea cucullata (776 ind.), gastropods Monodonta labio (468 ind.) and Batillaria multiformis (188 ind.) were the most common species on gravel and boulders substratum. Batillaria zonalis (130 ind.) was the most common species on sands and soft mud substrata.

Biodiversity and abundance of soft shore communities

3.6.67 Table 3.7 of Appendix O shows the mean values of species number, density, and biodiversity index H�� and species evenness J of soft shore communities at every tidal level and in every sampling zone. As mentioned above, the differences among sampling zones and tidal levels were determined by the major type of substratum primarily.

3.6.68 Among the sampling zones, the mean species number was varied from 15 - 18 spp. 0.25 m^-2 among the four sampling zones. The mean densities of ST (269 ind. m^-2) and TC3 (257 ind. m^-2) is higher than TC2 (247 ind. m^-2 TC1 (238 ind. m^-2). The higher densities of ST and TC3 are due to the relatively high number of individuals in each quadrat. The mean H�� for TC3 was 2.23, ST was 2.2, TC2 was 2.13 and TC1 was 2.07, followed by while the mean J of ST and TC3 was 0.8, slightly higher than TC1 and TC2 (0.77). This can be due to the relatively non-even taxa distribution.

3.6.69 In the present survey, no clear trend of mean species number, mean density, H�� and J observed among the tidal level.

3.6.70 Figures 3.14-3.17 of Appendix O show the temporal changes of mean species number, mean density, H�� and J at every tidal level and in every sampling zone along the sampling months. In general, all the biological parameters fluctuated seasonally throughout the monitoring period. Lower mean species number and density were recorded in dry season (December) but the mean H' and J fluctuated within a limited range.

3.6.71 From June to December 2017, there were steady decreasing trends of mean species number and density in TC2, TC3 and ST regardless of tidal levels. It might be an unfavorable change reflecting environmental stress. The heat stress and serial cyclone hit were believed to be the causes during the wet season of 2017. From March 2018 to December 2024 (present survey), generally increases of mean species number and density were observed in all sampling zones. It indicated the recovery of intertidal community.

Impact of the HKLR project

3.6.72 It was the 51st survey of the EM&A programme during the construction period. Based

3.6.72on the results, impacts of the HKLR project were not detected on intertidal soft shore

3.6.72community. Abnormal phenomena (e.g. rapid, consistent or non-seasonal decline of

3.6.72fauna densities and species number) were not recorded.

3.7 Solid and Liquid Waste Management Status

3.7.1 The Contractor registered with EPD as a Chemical Waste Producer on 12 July 2012 for the Contract. Sufficient numbers of receptacles were available for general refuse collection and sorting.

3.7.2 The summary of waste flow table is detailed in Appendix K.

3.7.3 The Contractor was reminded that chemical waste containers should be properly treated and stored temporarily in designated chemical waste storage area on site in accordance with the Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes.

Description of Activities	Site Area
Removal of Temporary Toe Loading Platform/Reinstatement Works	Portion X

	North Lantau Social Cluster
	NEL	NWL
Action Level	STG < 70% of baseline & ANI < 70% of baseline	STG < 70% of baseline & ANI < 70% of baseline
Limit Level	STG < 40% of baseline & ANI < 40% of baseline

	North Lantau Social Cluster
	NEL	NWL
Action Level	STG < 4.2 & ANI < 15.5	STG < 6.9 & ANI < 31.3
Limit Level	(STG < 2.4 & ANI < 8.9) and (STG < 3.9 & ANI < 17.9)

Ramboll Hong Kong Limited was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project until 30 September 2022.

ANewR Consulting Limited has been employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project with effective from 1 October 2022.

1 Introduction

1.1 Basic Project Information

1.1.4 BMT Hong Kong Limited was appointed by the Contractor to implement the EM&A programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.

1.1.6 This is the fifty-first Quarterly Environmental Monitoring and Audit (EM&A) report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 March 2025 to 31 May 2025.

1.2 Project Organisation

1.2.1 The project organization structure and lines of communication with respect to the on-site environmental management structure with the key personnel contact names and numbers are shown in Appendix A.

1.3 Construction Programme

1.3.1 A copy of the Contractor��s construction programme is provided in Appendix B.

1.4 Construction Works Undertaken During the Reporting Period

1.4.1 A summary of the construction activities undertaken during this reporting period is shown in

Table 1.1. The works areas of the Contract are showed in Appendix C.

2 EM&A Requirement

2.1 Summary of EM&A Requirements

2.1.1 The EM&A programme requires environmental monitoring of air quality, noise, water quality, dolphin monitoring and mudflat monitoring as specified in the approved EM&A Manual.

2.1.2 A summary of Impact EM&A requirements is presented in Table 2.1. The locations of air quality, noise and water quality monitoring stations are shown as in Figure 2.1. The transect line layout in Northwest and Northeast Lantau Survey Areas is presented in Figure 2.2.

2.2 Action and Limit Levels

2.2.1 Table 2.2 presents the Action and Limit Levels for the 1-hour TSP, 24-hour TSP and noise level.

2.2.2 The Action and Limit Levels for water quality monitoring are given as in Table 2.3.

2.2.3 The Action and Limit Levels for dolphin monitoring are shown in Tables 2.4 and 2.5.

2.3 Event Action Plans

2.3.1 The Event Actions Plans for air quality, noise, water quality, dolphin monitoring and mudflat monitoring and Action Plan for Landscape Works are annexed in Appendix D.

2.4 Mitigation Measures

2.4.1 Environmental mitigation measures for the contract were recommended in the approved EIA Report. Appendix E lists the recommended mitigation measures and the implementation status.

3 Environmental Monitoring and Audit

3.1 Implementation of Environmental Measures

3.1.1 Details of site audit findings and the corrective actions during the reporting period are presented in Appendix F.

3.1.2 A summary of the Implementation Schedule of Environmental Mitigation Measures (EMIS) is presented in Appendix E. Most of the necessary mitigation measures were implemented properly.

3.1.3 Regular marine travel route for marine vessels were implemented properly in accordance to the submitted plan and relevant records were kept properly.

3.1.4 Dolphin Watching Plan was implemented during the reporting period. No dolphins inside the silt curtain were observed. The relevant records were kept properly.

3.2 Air Quality Monitoring Results

3.2.2 No Action and Limit Level exceedances of 1-hr TSP were recorded at AMS5 and AMS6. No Action and Limit Level exceedances of 24-hr TSP were recorded at AMS5. No Limit level exceedances of 24-hr TSP was recorded at AMS6 whereas One Action Level exceedance of 24-hr TSP was recorded at AMS6.

3.3 Noise Monitoring Results

3.3.1 The monitoring results for construction noise are summarized in Table 3.3 and the monitoring results and relevant graphical plots for this reporting period are provided in Appendix H.

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.3.2 No Action/Limit Level exceedances for noise were recorded during daytime on normal weekdays of the reporting period.

3.3.3 Other noise sources during the noise monitoring included aircraft/helicopter noise, construction activities by other parties and human activities nearby.

3.4 Water Quality Monitoring Results

3.4.1 Impact water quality monitoring was conducted at all designated monitoring stations during the reporting period. Impact water quality monitoring results and relevant graphical plots are provided in Appendix O.

3.4.2 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

3.4.3 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

3.5 Dolphin Monitoring Results

Summary of Survey Effort and Dolphin Sightings

3.5.10 During the period of March to May 2025, six line-transect vessel surveys were conducted in NWL and NEL areas. All transect lines in each area were surveyed twice per month.

Encounter Rate

3.5.14 During this quarterly period, no dolphins were recorded while surveying the transect lines under favourable conditions (Beaufort 3 or better) (Table 3.4). The encounter rates averaged across all surveys were compared to the baseline monitoring period (September-November 2011) (Table 3.5).

3.5.22 As evidenced from encounter rate calculations, dolphin usage was markedly reduced in both NEL and NWL survey areas during the present quarterly period, when compared to the baseline period. A reduced occurrence of dolphins has been documented throughout the overall HZMB construction period.

Conclusion

3.5.24 During the present quarter of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White dolphins was noticeable from general observations.

3.6 Mudflat Monitoring Results

Sedimentation Rate Monitoring

3.6.2 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased.

Water Quality Monitoring

3.6.3 The mudflat monitoring covered water quality monitoring data. Reference was made to the water quality monitoring data of the representative water quality monitoring station (i.e. SR3(N)) as in the EM&A Manual. The water quality monitoring location (SR3(N)) is shown in Figure 2.1)

3.6.4 Water quality monitoring in San Tau (monitoring station SR3(N)) was conducted in March 2025 as part of mudflat monitoring. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS).

3.6.5 The water monitoring result for SR3(N) were extracted and summarised in Table 3.10:

3.6.13 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.

3.6.14 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

3.6.15 Data collected from direct counting and core sampling was pooled in every quadrat for data analysis. Shannon-Weaver Diversity Index (H��) and Pielou��s Species Evenness (J) were calculated for every quadrat using the formulae below,

where S is the total number of species in the sample, N is the total number of individuals, and Ni is the number of individuals of the ith species.

3.6.20 Figure 3.5 and 3.6 of Appendix O show the changes of number of individuals, meaning prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus in respectively in each sampling zone throughout the monitoring period.

Seasonal variation of horseshoe crab population

Box plot of horseshoe crab populations in TC3

Impact of the HKLR project

Discussion

3.6.53 All seagrass beds were observed disappeared at the monitoring sites during the December monitoring event in 2024. There were two typhoon/cyclone events that occurred during November 2024 which was an unusual local weather condition, and it may cause the disappearance of the seagrasses.

3.6.56 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.

3.6.59 In March 2021, an increased number of sea slugs and their eggs were observed in all sampling zones. It may due to the breeding season of sea slug and the increased of algae on the intertidal.

where S is the total number of species in the sample, N is the total number of individuals, and Ni is the number of individuals of the i^th species.